1. Field of the Invention
The present invention generally relates to a method and a system for improving performance of a mobile station in a wireless communication system, and more particularly to a method and a system for resource allocation in a wireless communication system including heterogeneous mobile stations using different resource allocation schemes.
2. Description of the Related Art
With rapid development of mobile communication technology, various communication systems providing high speed packet data services have been proposed. In design and control of communication systems, a main issue being focused on is optimization technology for effectively improving performance of the system. Therefore, recent mobile communication technologies have presented mathematical models for optimization of communication systems. Especially, various transmission control technologies have been proposed in order to effectively control resources which a base station allocates to mobile stations within an available bandwidth in a communication system.
In conventional transmission control technologies, optimization models for efficient resource allocation reflect ways of dealing with contentious traffic within a limited bandwidth regarding stability and fairness. Stability is an engineering field issue, which relates to randomness and feedback transmission, and fairness is an economic issue, which relates to utility. As networks gradually evolve to have intelligence, the difference between stability and fairness is gradually decreasing.
A conventional resource allocation method will now be described with an example of the data rate, which is a resource allocated to a mobile station by a base station.
As an example of the conventional technology of allocating resources to a mobile station by using a specific utility function, there is a treatise released in 1988, entitled “Rate Control For Communication Networks: Shadow Prices, Proportional Fairness And Stability (FP Kelly, University of Cambridge, UK).” Kelly's treatise (Kelly) proposed a distributed processing method that optimizes a specific utility function in order to maximize average fairness and throughput for each time unit during allocation of resources to the mobile station.
In Kelly, target formulas of the specific utility function are defined by Equations (1) and (2) below, and the distributed processing method is defined by Equation (3) below.
                    MAX        ⁢                              ∑            i                    ⁢                                          ⁢                                    U              i                        ⁡                          (                              x                i                            )                                                          (        1        )                                Ax        ≤        c                            (        2        )            
In Equation (1), U(x) denotes a utility function, x denotes a data rate (i.e. resource) allocated to a mobile station, and i denotes a parameter for identifying a mobile station (user). In Equation (2), A refers to a matrix indicating mobile stations, and c refers to the capacity of all resources that can be allocated by a base station. By using Equations (1) and (2), it is possible to allocate the data rate x to each mobile station to obtain a maximum utility function within the limited capacity c of the entire resources.
Further, Kelly has presented a shadow price defined by Equation (3) below, which is a parameter showing a change in Equation (1) when a condition such as the resource allocation cost is provided to Equation (1).
                                          μ            j                    ⁡                      (            t            )                          =                              P            j                    ⁡                      (                                          ∑                                  S                  :                                      jε                    ⁢                                                                                  ⁢                    S                                                              ⁢                                                          ⁢                                                x                  s                                ⁡                                  (                  t                  )                                                      )                                              (        3        )            
In Equation (3), xs refers to a data rate when the shadow price is applied, j denotes a parameter for identifying a base station, Pj denotes cost applied by the base station j when allocating a data rate, and μj refers to a shadow price when the base station j allocates a data rate.
Further, a data rate xr(t) allocated to a mobile station r when the shadow price as defined by Equation (3) is applied is defined by Equation (4) below.
                                          ⅆ                          ⅆ              t                                ⁢                                    x              r                        ⁡                          (              t              )                                      =                  K          ⁡                      (                                          W                r                            -                                                                    x                    r                                    ⁡                                      (                    t                    )                                                  ⁢                                                      ∑                                          jε                      ⁢                                                                                          ⁢                      r                                                        ⁢                                                                          ⁢                                                            μ                      j                                        ⁡                                          (                      t                      )                                                                                            )                                              (        4        )            
In Equation (4), parameter r is used with the same purpose as that of i for identifying a mobile terminal in the target Equation (1), W refers to the price charged to a corresponding mobile station r for use of a packet data service during unit time, and K denotes a constant. Equation (4) can provide proportional fairness in transmission control technology of an Additive Increase Multiplicative Decrease (AIMD) scheme, in which a bandwidth is multiplicatively reduced in a congestion status and is additively increased in a non-congestion status in a network using a specific utility function.
An example of communication systems for allocating a data rate to a mobile station is the 1x Evolution Data Only (EV-DO) proposed by 3GPP2, which is one of standard organizations. When the 1x EV-DO system controls the forward data rate, the mobile station measures a reception intensity of a pilot channel transmitted by the base station, and transmits a message including Data Rate Control (DRC) information used by the mobile station to the base station based on the measured reception intensity of the pilot channel signal. Then, the base station receives the DRC information from mobile stations and performs resource allocation in order to transmit packet data to only mobile stations in a good channel condition with a data rate reported by the corresponding mobile station.
Therefore, in the 1x EV-DO system, multiple mobile stations transmit DRC information in the same way, and the base station allocates a reported data rate to only the mobile stations in a good channel condition from among the mobile stations that transmitted DRC information. That is, the base station applies a specific utility function. Therefore, it is noted that the 1x system shows the AIMD characteristic, as shown in FIGS. 1 and 2.
The conventional technology as described above is proper for resource allocation in a wireless communication environment applying a common specific utility function to all mobile stations communicating with a base station. However, the conventional technology is improper for a wireless communication environment including heterogeneous mobile stations using different protocols for resource allocation. Therefore, a need exists for a resource allocation method for the future wireless communication environment which applies an unspecified utility function for allocation of resources to heterogeneous mobile stations.